Effects of Sublethal Exposure to Piper aduncum L. Essential Oil on Population Growth of Stored-Product Insect Pests

Botanical insecticides, such as essential oils, have drawn increasing interest in pest management. However, sublethal effects on exposed individuals and their offspring are often overlooked. This study evaluated the population growth of Sitophilus zeamais, Oryzaephilus surinamensis, Cryptolestes ferrugineus, and Tribolium castaneum in maize grains exposed to sublethal concentrations (1/3 and 2/3 of the LC₅₀) of Piper aduncum L. essential oil (PAEO). Population growth was assessed using daily emergence curves, total adult emergence, and grain mass loss. Sublethal PAEO exposure reduced and delayed population growth of S. zeamais, C. ferrugineus, and T. castaneum. At 2/3 of the LC₅₀, total adult emergence decreased by 42.6% in S. zeamais and 40.2% in T. castaneum compared with the control. In contrast, O. surinamensis showed an accelerated and increased emergence response, with a maximum of 10.67 ± 1.24 adults day^-1 at 2/3 of the LC₅₀, representing a 174.3% increase relative to the control, consistent with a possible hormetic response. These findings demonstrate species-specific responses to sublethal PAEO exposure, with population growth suppressed in three species but stimulated in O. surinamensis. This highlights the importance of appropriate dose selection to maximize pest suppression and avoid unintended stimulatory effects under stored-grain conditions.